1. Field of the Invention
The invention relates to an orthopaedic fluid damper and to an orthopaedic aid with such a damper which is designed for use in a prosthesis or orthesis, with a displacement chamber formed in a cylinder housing, with a piston mounted in the displacement chamber, with a fluid reservoir for a fluid, with a backflow line which connects the displacement chamber to the fluid reservoir, and with a valve which can assume an opening position and a closing position, in which it at least partially closes the backflow line. According to a further aspect, the invention relates to a method for controlling the orthopaedic aid.
2. Description of Related Art
Orthopaedic fluid dampers are employed in orthopaedic aids, such as, for example, prostheses or ortheses. They serve as a resistance element between two limbs. For example, the orthopaedic fluid damper is arranged between a thigh and a lower leg of a leg prosthesis and increases a bending resistance of a knee joint of the leg prosthesis.
Leg prostheses with orthopaedic fluid dampers of this type are rarely found in geriatric patients. For patients of great age who are severely restricted in their muscular and motor capability, blocking knee joints are often employed.
Known orthopaedic blocking knee joints for geriatric leg prostheses provide geriatric patients with only two states, blocked or unblocked, for cost reasons. The geriatric patient prefers the blocking knee joint which is blocked by means of the lock. Known orthopaedic blocking joints have the disadvantage that they cause the patient's gait to have a hobbling appearance, since the patient brings the leg forward by rotating it outwardly (circumduction) or lengthens the healthy leg via a pointed-foot position or slanted-hip position, so that the leg prosthesis can swing through freely. So that he can sit down, the geriatric patient releases the lock manually. In this state, the leg prosthesis offers no bending resistance and therefore, disadvantageously, also no longer any safety. The patient has to support himself with both hands in this situation. Moreover, should the geriatric patient stumble when the leg prosthesis is released, he involuntarily falls down. For this reason, known orthopaedic aids which are equipped with conventional orthopaedic locks are unpopular among geriatric patients.
EP 0 309 441 discloses a double-acting hydraulic piston/cylinder unit, by means of which the outer dimensions of a concertina preserve an approximately predetermined form, the concertina spanning large parts of the piston/cylinder unit. The disadvantage of this piston/cylinder unit is that it is complicated to produce.
DE 102 14 357 A1 discloses a prosthetic knee joint with a hydraulic damping cylinder. In the prosthetic knee joint, a hydraulic fluid is present, the viscosity of which can be varied via an external force field. The disadvantage of this embodiment is that, although it makes increased walking comfort possible, it nevertheless requires an electric control, which, however, is not justifiable for low-priced prostheses.
DE 198 59 931 A1 discloses a leg prosthesis which is likewise damped to a greater or lesser extent via a hydraulic fluid, the viscosity of which can be varied by means of external electrical fields. The disadvantage here, too, is that a control is necessary.